543

 To know how many times the values of a given column repeat
 themselves, use the function COUNT. I'm using a example
 from the database notes. Real data.
 ----------------------------------------------------------
 SELECT COUNT(k1) AS repeats FROM notes GROUP BY k1;

 Output excerpt:
 +-------------------------*---------*
 | k1                      | Repeats |
 +-------------------------+---------+
 | arch                    |       1 |
 | backblaze               |       2 |
 +-------------------------+---------+
 ----------------------------------------------------------